The leader of France's main far-right party has said that she is demanding a recount after her razor-thin loss to a Socialist in northern France as part of nationwide legislative elections.

Marine Le Pen told France-Info radio that her anti-immigration National Front party will appeal to France's Constitutional Council after results showed she lost to Socialist Philippe Kemel by 118 votes out of more than 55,000 cast.

The result in the northern Pas-de-Calais region came as French voters vaulted president Francois Hollande's Socialists and their close allies into control of the 577-seat National Assembly in Sunday's voting.

The National Front won two seats - its best showing in the Assembly since the late 1980s.